Mediation for synchronous replication

Abstract

Determining active membership among storage systems synchronously replicating a dataset, where determining active membership includes: detecting, by a particular storage system of the storage systems, a communication fault with one or more of the storage systems, where the particular storage system is configured to request mediation from a mediation target; determining that at least one of the one or more storage systems is configured to request mediation from the mediation target responsive to the communication fault; and responsive to determining that one or more of the storage systems is configured to request mediation from the mediation target, determining whether to request mediation from the mediation target.

What is claimed is: 
     
       1. A method comprising:
 detecting, by a particular storage system, that a quorum cannot be established for a set of storage systems; and 
 responsive to detecting that quorum cannot be established and determining that one or more of the storage systems is configured to request mediation from a mediation target, determining, by the particular storage system, whether to request mediation from the mediation target. 
 
     
     
       2. The method of  claim 1 , further comprising determining whether to request mediation from the mediation target comprising determining to request mediation, wherein the mediation target is configured to mediate between sets of storage systems that are unable to form a quorum. 
     
     
       3. The method of  claim 1 , further comprising determining whether to request mediation from the mediation target comprising determining to not request mediation. 
     
     
       4. The method of  claim 1 , wherein each storage system of the storage systems corresponds to zero or more votes within a quorum protocol that determines whether a first set of one or more storage systems may detach a second set of one or more storage systems. 
     
     
       5. The method of  claim 4 , wherein a respective quantity of votes corresponding to a respective storage system is dependent upon storage system characteristics. 
     
     
       6. The method of  claim 4 , further comprising:
 determining, by the first set of one or more storage systems, that there is consistent communication among storage systems of the first set of one or more storage systems; 
 determining, by the first set of one or more storage systems, lack of communication with storage systems among the second set of one or more storage systems, wherein the first set of one or more storage systems is unable to form a quorum; and 
 determining, by the first set of one or more storage systems, that the second set of one or more storage systems is unable to form a quorum. 
 
     
     
       7. The method of  claim 6 , further comprising:
 determining that the first set of one or more storage systems is unable to form a quorum in dependence upon the first set of one or more storage systems including exactly half of the votes for the storage systems synchronously replicating the dataset. 
 
     
     
       8. The method of  claim 6 , further comprising:
 determining that the second set of one or more storage systems is unable to form a quorum in dependence upon the second set of one or more storage systems including half of the votes for the storage systems synchronously replicating the dataset. 
 
     
     
       9. The method of  claim 6 , further comprising determining whether to request mediation from the mediation target dependent upon the first set of one or more storage systems being unable to obtain a quorum and no other set of the one or more storage systems being able to obtain a quorum. 
     
     
       10. An apparatus comprising a computer processor, a computer memory operatively coupled to the computer processor, the computer memory having disposed within it computer program instructions that, when executed by the computer processor, cause the apparatus to carry out the steps of:
 detecting, by a particular storage system, that a quorum cannot be established for a set of storage systems; and 
 responsive to detecting that quorum cannot be established and determining that one or more of the storage systems is configured to request mediation from a mediation target, determining, by the particular storage system, whether to request mediation from the mediation target. 
 
     
     
       11. The apparatus of  claim 10 , further comprising computer program instructions that, when executed by the computer processor, cause the apparatus to carry out determining whether to request mediation from the mediation target comprising determining to request mediation, wherein the mediation target is configured to mediate between sets of storage systems that are unable to form a quorum. 
     
     
       12. The apparatus of  claim 10 , further comprising computer program instructions that, when executed by the computer processor, cause the apparatus to carry out determining whether to request mediation from the mediation target comprising determining to not request mediation. 
     
     
       13. The apparatus of  claim 10 , wherein each storage system of the storage systems corresponds to zero or more votes within a quorum protocol that determines whether a first set of one or more storage systems may detach a second set of one or more storage systems. 
     
     
       14. The apparatus of  claim 13 , wherein a respective quantity of votes corresponding to a respective storage system is dependent upon storage system characteristics. 
     
     
       15. The apparatus of  claim 13 , further comprising computer program instructions that, when executed by the computer processor, cause the apparatus to carry out the steps of:
 determining, by the first set of one or more storage systems, that there is consistent communication among storage systems of the first set of one or more storage systems; 
 determining, by the first set of one or more storage systems, lack of communication with storage systems among the second set of one or more storage systems, wherein the first set of one or more storage systems is unable to form a quorum; and 
 determining, by the first set of one or more storage systems, that the second set of one or more storage systems is unable to form a quorum. 
 
     
     
       16. The apparatus of  claim 15 , further comprising computer program instructions that, when executed by the computer processor, cause the apparatus to carry out the steps of:
 determining that the first set of one or more storage systems is unable to form a quorum in dependence upon the first set of one or more storage systems including exactly half of the votes for the storage systems synchronously replicating the dataset. 
 
     
     
       17. The apparatus of  claim 15 , further comprising computer program instructions that, when executed by the computer processor, cause the apparatus to carry out the steps of:
 determining that the second set of one or more storage systems is unable to form a quorum in dependence upon the second set of one or more storage systems including half of the votes for the storage systems synchronously replicating the dataset. 
 
     
     
       18. The apparatus of  claim 15 , further comprising computer program instructions that, when executed by the computer processor, cause the apparatus to carry out determining whether to request mediation from the mediation target dependent upon the first set of one or more storage systems being unable to obtain a quorum and no other set of the one or more storage systems being able to obtain a quorum.